c)The mesoderm of the neurula stage embryo can be divided into
five regions.The
________________________ forms the notochord.

d)Some regions of the limb bud have been defined as having
important roles during limb development.The _________________________ consists of rapidly dividing mesenchymal
cells at the distal end of the limb bud.These cells stop proliferating if the __________________________ is
surgically removed from the limb bud.

e)Mice that carry a deletion in the _________________________
gene have foot pads (ventral structures) on the dorsal surface of their feet.

f)In the peripheral nervous system, axons are often bundled in
nerve fibers, and neuronal cell bodies are clustered in
__________________________.

g)______________________________ are secreted by target
cells.They are chemoattractants for
migrating cells or growth cones, and they suppress apoptosis.

h)During gastrulation, the ectodermal cells expand to cover the
outside of the embryo via a process called ___________________________.

i)During mammalian gastrulation, individual cells migrate into
the blastocoel.This type of cell
movement is called ________________________.

List of Possible Answers for Questions on page 1

Agrins

Axin

Apical Ectodermal Ridge

Blastocoel

Chordamesoderm

Convergent Extension

Dendrites

Desert Hedgehog

Epiblast

Epiboly

Fibers

Fibroblast Growth Factor

Floorplate

Frizzled

Ganglia

Growth cones

Henson's Node

Hox11c

Hypoblast

Ingression

Involution

Involuting Mesoderm

Lateral plate mesoderm

LRP5/6

Midblastula Transition

Netrins

Neural ectoderm

Neurotropins

Patched

Posterior Marginal Zone

Progress Zone

Roofplate

Soma

Somitic mesoderm

Somite

Survivins

Trophoblast

Tyrosine kinase

Wnt7a

Zone of Polarizing Activity

Part 2.70 points.

1.(12 points)

Describe two cells that migrate to their final location
during mammalian embryogenesis.For
each, describe (a) where the cell initiates its migration; (b) where it
migrates to; and (c) its function after it completes migration and
differentiates.

Cell 1

a)

b)

c)

Cell 2

a)

b)

c)

2)10 points

Dickkopf (Dkk1) protein is produced by Spemann's
Organizer.Describe

a)It's developmental function (What is the loss-of-function
phenotype; What aspect of Organizer function does it mediate?)

b)It's biochemical function (What does it bind, inhibit, or
activate?).

3.(20 points)

The cells of the Zone of Polarizing Activity secrete Sonic
Hedgehog.When researchers stain a limb
bud with a Shh-specific antibody, Shh expression appears to be restricted to
the Zone of Polarizing Activity.However, it is possible that Shh is present beyond the ZPA at levels
below the level of antibody detection.

(a)Design an experiment to test the hypothesis that Shh acts as a
morphogen to pattern the limb bud.(10
pts)

(b)Describe two possible results of this experiment.For each, explain how you would interpret
the result. (10 pts)

4. (15 points)

The flat bones in the skull are formed by a mechanism that
is fundamentally different from endochondral ossification, the process by which
the rest of our bones are formed.

a)Describe skull bone formation.Describe the role of at least one cell type.

b)Describe endochondral ossification, including a description of
at least two cell types involved in this process.

c)Describe "growth
plates".Why do our long bones
eventually stop growing?

5.(13 points)

Some of the cells in the neural tube will form neurons,
while others will form glial cells.This cell fate decision is regulated by Notch signaling.If Notch signaling is inhibited, then excess
neurons form.

(a)Does Notch function as a ligand or as a receptor (2 pts)?

(b)Assume that the
cells below belong to an equivalence group in the neural tube.Mark the cells that will form neurons with
an "N". Note that one cell has already been specified. (5 points)

(c)For the equivalence
group diagramed below, assume that the cells in row 4 have a mutation in Notch.Mark the cells that will form neurons with
an "N".You may choose to
explain your reasoning, but it is not required.(6 points)